The present invention relates generally to pressure responsive valves for use in subsurface operations, and more particularly relates to pressure actuated valves particularly well suited for use below a packer in a subsurface well.
Subsurface valves are commonly utilized in the oil and gas industry to establish a flow path between the interior of a conduit and the exterior of a conduit. In particular, such valves are commonly utilized to establish a flow path between the interior of a tubing string and the well annulus. Where such valves are placed in a tool string below the packer, they are typically referred to as "vents." Conventional vents are either mechanically actuated or pressure actuated. Where the vents are mechanically actuated, movement of the valve member in the vent is accomplished either by mechanical movement of an actuation member, or by the mechanical breaking of pressure kobes, to allow existing hydraulic pressures to operate the valve member. An example of this latter type of valve is disclosed in U.S. Pat. No. 4,576,233, issued to Flint R. George, and assigned to the assignee of the present invention. Where conventional vents are pressure actuated, they are typically responsive either to pressure inside the tubing string, or to pressure supplied to the vent through a dedicated conduit, such as a control line, external to the tubing string.
The use of conventional tubing pressure-actuated vents is not always desirable in perforating operations. In many perforating operations, it will be desired to perforate the well with an underbalance (i.e., with a pressure in the tubing string which is less than the anticipated formation pressure). In many such operations, after the tubing pressure has been raised to actuate the vent, the pressure must be reduced to a lower desired level to establish the desired under-balance. Where this pressure in the tubing string is also to be utilized to actuate the perforating gun, such an operation typically requires that the pressure be established through use of nitrogen, which requires utilizing auxiliary nitrogen units on-site. Such operations typically do not provide an opportunity for use of other conventional methods of reducing pressure to the well, such as swabbing the well, even if a time delay firing head were utilized.
Where pressure from a control line is utilized to actuate a vent, the provisions for the control line running along the exterior of the tubing make assembly of the string undesirably complex. The assembly of such a structure becomes especially time consuming, and therefore costly, where a long interval is to be established between the packer and the vent, which will typically be located generally proximate the perforating gun firing head. Such long intervals are common in highly deviated, or in horizontal wells.
Accordingly, the present invention provides a new method and apparatus for actuating a vent through use of pressure in the well annulus above the packer whereby the vent may be placed at any desired location relative to the packer without significantly complicating the assembly of the tool string.